1. Technical Field
The present invention relates to a flexible display device and a method for manufacturing the flexible display device. More particularly, the present invention relates to a flexible display device and a manufacturing method with improved reliability and reduced defect.
2. Description of the Related Art
In the display device market, a flat panel display (FPD) has replaced a Cathode Ray Tube (CRT) monitor and becomes popular. The FPD includes, for example, a liquid crystal display (LCD), a plasma display panel (PDP) or an organic electro luminescence display (OLED). The FPD is lighter and thinner than the CRT. The FPD may be easily applied to large size display systems or portable display systems. A glass substrate has been used in the FPD because it can endure high temperature applied in the manufacturing processes. Due to the rigid properties under the room temperature, the glass substrate may not be suitable for the flexible display device. Recently, flexible materials are used for the FPD to develop the flexible display device which can be rolled or folded. Such flexible display device may be deformed in any conditions. Using a flexible material such as plastic film, the flexible display device having the same displaying performance in the rolled or bent state becomes popular.
FIG. 1 illustrates a flow chart showing a manufacturing method of a flexible display device according to the related art. Referring to FIG. 1, the manufacturing method includes an adhering process (S1), a display panel forming process (S3) and a peeling-off process (S5). In the adhering process (S1), a rigid substrate is temporarily attached to the back surface of a flexible substrate for supporting the flexible substrate rigidly during the manufacturing process. It is also easy to handle the flexible substrate. The rigid supporting substrate adhering to the back surface of the flexible substrate further secures the flexible substrate and prevents distortion or deformation of the flexible substrate. With the supported flexible substrate provided by the adhering process (S1), it is possible to carry out the display panel forming process (S3) more precisely in a stable manner.
The display panel forming process (S3) includes processes for forming various patterns which will become driving elements of a display panel. For example, for the flexible display device which is driven by the thin film transistor (TFT), the TFT array should be formed on the flexible substrate. The peeling-off process (S5) separates the supporting substrate and adhesives from the flexible substrate after completing the display panel forming process (S3). The rigid supporting substrate is temporarily attached during the adhering process (S1) and is removed from the flexible substrate after completing the display panel forming process (S3). Removal of the rigid supporting substrate may maximize flexible property of the flexible display device.
The adhesives preferably may not be fully hardened during the display panel forming process (S3) to peel off the flexible substrate from the rigid supporting substrate easily. The upper most limitation of the temperature for the display panel forming process (S3) is less than 150° C. However, it may differ depending on the kind of adhesives. The TFT driving elements formed under 150° C. may experience degraded performance. Driving voltages of the TFT may not be stable, which may affect the reliability of the flexible display device.
Further, in the adhering process (S1), it is undesirable to have air bubbles formed between the flexible substrate and the adhesive layer. The air bubbles may degrade the reliability of the display panel forming process (S3). Additional equipment may be used to apply the adhesive layer between the flexible substrate and the rigid supporting substrate without forming the air bubbles. The development and use of this equipment can increase manufacturing expenses. The adhesives may not be perfectly removed from the flexible substrate in the peeling-off process (S5). The TFT patterns may be damaged by the force which separates the flexible substrate from the rigid supporting substrate. The pattern that is damaged during the peeling-off process (S5) degrades the reliability of the display device. Accordingly, there is a need for a method for manufacturing a flexible display device which obviates drawbacks of the related art.